How to Read a Barometer (Mercury Type)

Figure 7

Corrections to be Made to the Observed Barometer Reading

(See "Lange's Handbook of Chemistry" 11th ed., 1973 pp. 2-29 to 2-34 for more details).

The mercury column and the walls of the barometer (glass or brass depending on the type of barometer) expand at different rates. The value listed in the table below is to be subtracted from the observed barometer reading at the temperature listed (measure the air temperature with a thermometer at the time you read the barometer).

BRASS SCALE CORRECTIONS

pressure (torr)

temp. (°C) 720. 730. 740. 750.

20. 2.3 2.4 2.4 2.4

21. 2.5 2.5 2.5 2.6

22. 2.6 2.6 2.7 2.7

23 2.7 2.7 2.8 2.8

24. 2.8 2.9 2.9 2.9

25. 2.9 3.0 3.0 3.1

26. 3.0 3.1 3.1 3.2

27. 3.2 3.2 3.2 3.3

28. 3.3 3.3 3.4 3.4

29. 3.4 3.4 3.5 3.5

30. 3.5 3.6 3.6 3.7